Japanese Patent Application Laid-open Publication No. 2008-14095 (hereinafter referred to as “the relevant patent literature”) discloses a vehicular keyless apparatus including a mobile device and a vehicle-mounted device. The vehicle-mounted device includes a control section as a control device, and the control section is connected to a communication section having, for example, an LF (Low Frequency) transmission section, a vehicular external antenna output section and antennas. Further, according to the disclosure of the relevant patent literature, once it is determined that the mobile device is currently at a stop within a first search range (first transmission area) set outside of the vehicle via one of the antennas, the control section lowers transmitter power output of electromagnetic waves transmitted from the antennas in such a manner that the above-mentioned first search range is narrowed to a second search range (second transmission area) until no more response is received from the mobile device.
Namely, when a user or passenger having the mobile device with it (i.e., her or him) has no intention to get in the vehicle, the vehicle-mounted device shifts to an electric power saving mode. Then, as the passenger approaches the vehicle, i.e., as the mobile device enters the second search range narrowed from the first search range, the vehicular keyless apparatus can not only unlock the doors of the vehicle but also illuminates a region around the feet of the passenger.
However, after the first search range has been narrowed to the second search range, the passenger having the mobile device with it (her or him) may sometimes move or get away from the vehicle out of the first search range. In such a situation, the vehicular keyless apparatus cannot unlock the doors. Namely, after the first search range has been narrowed to the second search range, the passenger has to approach the vehicle until it enters the second or narrowed search range, in order for the vehicular keyless apparatus to unlock the doors.